Components which rotate at high speed, in particular rotors of steam turbines, or else other turbines, must be subjected from time to time to an inspection in which, in particular, the rotor of the turbine is examined for cracks. Cracks such as these often occur in circumferential blade slots, in which the blades of the turbine are held against the centrifugal forces that occur. Inspections such as these are frequently carried out using ultrasound sensors which are in the form of single-channel or multi-channel ultrasound measurement heads (phased arrays) and carry out delay-time duration determinations (so-called UT/PA/TOFD technology). During the inspections, one or two ultrasound sensors must be moved with great accuracy along the feet of the blades which are mounted in the rotor, in order to scan the critical area of the rotor, specifically the circumferential slots.
In order to allow good reproducibility of the results and a good quality of the determined data to be achieved during these inspections, the inspection should be linked to an appropriate position determination. Motorized inspection is a major advantage, on the one hand, because of the reproducible speed of travel, which can be maintained accurately, and, associated with this, the better reproducibility of the measurement results, and on the other hand because of the poor accessibility to the regions to be inspected (between the blade rows).
Since, during inspections such as these in the slots between the blade rows, the annular sealing strips which are present there in the slot base are often not removed in advance, they represent a serious obstruction to automated inspection.
Until now, it has been normal practice to carry out such inspections manually or with the sealing strips being removed before the inspection, and with the sealing strips being reinserted after the inspection. However, a process such as this is time-consuming, provides only a restricted data quality and results which cannot be reproduced well, while being impeded by a lack of accessibility.
A stationary robot arm has also already been used. In its application, the robot arm is highly flexible, but is dependent on having a large robot and requires a long setting-up time. However, it is particularly disadvantageous that the rotor to be inspected must be rotated, necessitating a (heavy and expensive) rotation mechanism.
Mobile scanners can move over the circumference of the rotor and carry out the required inspection in the process. These mobile scanners are generally equipped with broad magnetic wheels, which means that they cannot cope with obstructions which occur on the circumference of the rotor, in particular with annular sealing strips, a number of which may be present, and some of which may be separated by only 9 mm.